The present invention relates to a sheet guide apparatus which is connected to a printing press for printing a sheet, a coating machine for coating the sheet, or the like, and conveys the sheet in a stable state.
Generally, in a delivery device for a sheet-fed perfecter, a sheet guide member is arranged around a delivery cylinder to prevent rubbing or wrinkles which cause a printing trouble during sheet conveyance. To convey a sheet in a stable state, the sheet guide member blows air in a direction perpendicular to the sheet convey direction. In the conventional sheet guide apparatus which has the above arrangement, problems occur when a so-called thick sheet having a relatively large thickness is to be conveyed around the delivery cylinder. More specifically, because the thick sheet does not flex readily and is heavy, a large centrifugal force is generated to bring the printing surface on the reverse side of the trailing edge of the sheet into contact with the sheet guide member to damage or rub the printing surface.
In order to prevent these problems, if the gap between the outer surface of the delivery cylinder and the sheet guide member is increased, the Venturi effect obtained by the air blown from the sheet guide member decreases. When a so-called thin sheet having a relatively small thickness is to be conveyed, instability occurs to the sheet to damage or rub the printing surface.
As a countermeasure to solve these problems, as shown in Japanese Patent Laid-Open No. 2004-137028, a structure is proposed in which the distal end of the sheet guide member upstream in the sheet convey direction is movable between positions close to and spaced apart from the delivery cylinder. In this structure, when a thin sheet is to be conveyed, the distal end of the sheet guide member upstream in the sheet convey direction is moved close to the delivery cylinder. When a thick sheet is to be conveyed, the distal end of the sheet guide member upstream in the sheet convey direction is spaced apart from the delivery cylinder.
In the conventional sheet guide apparatus proposed in the above reference, when the distal end of the sheet guide member upstream in the sheet convey direction is positioned spaced apart from the delivery cylinder in order to convey a thick sheet, that portion of the sheet guide member which is downstream in the sheet convey direction stays close to the delivery cylinder. Therefore, when the thick sheet is to be gripped and conveyed by the grippers of the delivery cylinder, the trailing edge of the thick sheet which is to be spaced apart from the delivery cylinder is brought into contact with the inner surface of the sheet guide member downstream in the sheet convey direction by the centrifugal force to damage or rub the printing surface on the reverse side of the sheet.